The present invention relates to a secondary battery including a cathode, an anode, and an electrolyte and an electronic device including a secondary battery.
In recent years, portable electronic devices such as a video camera, a digital still camera, a mobile phone, and a notebook personal computer have been widely used, and it is strongly demanded to reduce their size and weight and to achieve their long life. Accordingly, as a power source for the portable electronic devices, a battery, in particular, a light-weight secondary battery capable of providing a high energy density has been developed.
Specially, a secondary battery using insertion and extraction of lithium ions for charge and discharge reaction (so-called lithium ion secondary battery) is in practical use widely, since such a lithium ion secondary battery is able to provide a higher energy density than a lead battery and a nickel cadmium battery.
The lithium ion secondary battery includes an electrolyte together with a cathode and an anode. The cathode has a cathode active material layer containing a cathode active material on a cathode current collector. The anode has an anode active material layer containing an anode active material on an anode current collector. The electrolyte contains a solvent and an electrolyte salt dissolved therein.
As the anode active material, a carbon material such as graphite is widely used. In the carbon material, the crystal structure change at the time of inserting and extracting lithium ions is very little. Therefore, a battery capacity and the like are able to be stably obtained.
In recent years, as the high performance and the multi functions of the portable electronic devices are developed, further improvement of the battery capacity is demanded. Thus, it has been considered to use a high capacity material such as silicon and tin instead of the carbon material. Since the theoretical capacity of silicon (4199 mAh/g) or the theoretical capacity of tin (994 mAh/g) is significantly higher than the theoretical capacity of graphite (372 mAh/g), it is prospected that the battery capacity is thereby highly improved.
However, in such a lithium ion secondary battery, at the time of charge and discharge, the anode active material inserting lithium ions becomes highly active. Thus, the electrolyte becomes easily decomposed, and part of lithium ions becomes easily inactive. Thereby, battery characteristics such as sufficient cycle characteristics and swollenness characteristics are hardly obtained. Such a problem is significant in the case where the high capacity material is used as an anode active material.
To solve the foregoing problems of the lithium ion secondary battery, various studies have been made. For example, a technology to improve battery characteristics such as high temperature characteristics, storage characteristics, and cycle characteristics by containing various additives into an electrolyte has been proposed. As the additive, phenylsulfonic metal salt (for example, refer to Patent document 1), organic alkali metal borate (for example, refer to Patent document 2), 1,5-naphthaline-disulfonic sodium (for example, refer to Patent document 3), a compound containing a cyanoethyl group such as 2-cyanoethyl propionate (for example, refer to Patent document 4), a compound having a sulfonyl group and an unsaturated bond (for example, refer to Patent document 5) and the like are used. In addition, an aromatic compound such as biphenyl, terphenyl, cyclohexyl, benzene, and a derivative thereof is also used (for example, refer to Patent documents 6 to 9). Further, a technology of coating a surface of an electrode (specially a cathode) with an aliphatic nitrile compound such as adiponitrile in order to prevent thermorunaway at the time of overcharge (for example, refer to Patent document 10) or a technology of coating a surface of a carbon material used as an anode active material with a lithium alkoxide compound such as ethanediol dilithium in order to prevent lowering of battery capacity (for example, refer to Patent document 11) have been also proposed.